It crushes Keith Hernandez to see his beloved Mets exhibit a nonchalant attitude about the importance of defense at his former position.

The former Gold Glove-winning first baseman zinged the Amazin’s during Wednesday’s 4-3 road loss to the Brewers about the team’s lack of emphasis on having a good glove at first base.

“It seems like in today’s game, they don’t give first base enough credit,” Hernandez said during showing Brewers first baseman Andrew Vaughn stretching for an out .

“Certainly, the Mets don’t.”

Hernandez is known for valuing fundamentals — “good fundies,” as he calls them — and often criticizes teams during broadcasts when they turn into the “Bad News Bears.”

The Mets employed Pete Alonso at first base for the previous seven seasons, and though no one would confuse Alonso for a Gold Glover, he worked hard to be serviceable or better.

This season, the Mets have taken the “Moneyball” idea of first base being “not that hard” and hoping that a rotating cast of players can provide manageable defense.

Mark Vientos has struggled at first base. Robert Sabo for NY Post

The Mets rank 23rd in defensive runs saved with a -3 mark, according to FanGraphs.

The team uses Mark Vientos at the position though he’s better served as a designated hitter and has employed Jorge Polanco though he had minimal experience in his lengthy career.

Jared Young and Eric Wagaman have also had their turn.

Baseball Savant ranks Young (+1), Polanco (0), Wagaman (-1) and Vientos (-8) in terms of their effectiveness as measured by outs above average.

Keith Hernandez flashing the leather at first base. Getty Images

It would be one thing if the Mets were offsetting that lack of defensive with offensive production, like they did in the Alonso years, but their first basemen this year aren’t holding up their end of the bargain.

They are slashing .220/.281/.397 and have a combined -0.6 fWAR, ahead of only the Diamondbacks.

The ineffectiveness both offensively and defensively from their first basemen is a reason why the Mets are 43-60 and in last place in the NL East and sure to be trade deadline sellers.